Fixed capitalization in s:InitDict()

I fixed `s:InitDict()` behaviour.

**Expected behavior:**
`s:InitDict()` capitalize the key code string

**Current behavior:**
`s:InitDict()` uppercase whole key code string

**For example:**
*before `call <SID>InitDict('g:Lf_CommandMap', s:Lf_CommandMap) ` ([plugin/leaderf.vim#L145](https://github.com/sgur/LeaderF/blob/master/plugin/leaderf.vim#L145))*
~~~ vim
let g:Lf_CommandMap = {
      \   '<down>': ['<Down>', '<C-J>', '<C-N>']
      \ , '<up>': ['<Up>', '<C-K>', '<C-P>']
      \ }
~~~
*after `call <SID>InitDict('g:Lf_CommandMap', s:Lf_CommandMap)`*
~~~ vim
let g:Lf_CommandMap = {
      \ ... <snip>,
      \ '<DOWN>': ['<DOWN>', '<C-J>', '<C-N>'],
      \ '<UP>': ['<UP>', '<C-K>', '<C-P>'],
      \ ... <snip>
      \ }
~~~
this uppercased string cannot be accepted by  `startExplAction()` in `manager.py`